The full potential for fuel savings of hydraulic hybrid vehicles has yet to be realized due to a disconnect between controller design and system design. Previous research has only used optimal control to baseline control strategies as a means for creating better implementable controllers. However, the utility of optimal control extends well beyond controller design. This thesis merges this concept with system design, and in doing so prove the effectiveness of designing a hydraulic hybrid vehicle using optimal control to minimize fuel consumption.

The design chosen for study is the series hydraulic hybrid. The design variables selected for investigation are the primary unit size, secondary unit size, accumulator volume, and minimum system pressure. A review of traditional static sizing is conducted, and a new novel approach to selecting the minimum system pressure is derived on an energy density basis.

An optimally controlled series hybrid environment is created using deterministic dynamic programming. In it a parameter variation study is conducted investigating a broad range of the design variables. As a result, the fuel economy of each system can be compared fairly without sensitivity to suboptimal controller variations. The algorithm systematically develops optimal control decisions unique to each design, and in doing so showcases every design to its fullest potential.

The results evaluate the effectiveness of the statically sized system in terms of fuel economy for a representative driving schedule. In addition, trends pertaining to the accumulator volume, secondary unit, primary unit, and minimum system pressure are determined.

A series hybrid test rig was also developed as a means of testing future control strategies for the series hydraulic hybrid. Special considerations pertaining to testing this type of system are considered. Test results showing hybrid proof of concept are included.